an automated method for the aerodynamic modelling …€¦ · “the influence of rotating wheels...
TRANSCRIPT
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AN AUTOMATED METHOD FOR THE AERODYNAMIC MODELLING
OF GROOVED TIRES
An efficient solution for the modelling of complex motion in vehicle applications
Thomas Schumacher, Pavlos Alexias
GOFUN
22/04/2020
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Overview
› Moving Reference Frames (MRF)− Rotation Approximation
− Only rotationally symmetric zones
− Convergence Slowdown
› Refactoring + Extended Functionality
› Two main features1. More Accurate + Easier Tire Modelling
2. Vehicle Cornering
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Introduction | Tire Modelling
Wäschle, A., “The Influence of Rotating Wheels on Vehicle Aerodynamics - Numerical and Experimental Investigations”, SAE World Congress & Exhibition, (SAE International, Apr. 2007), doi: 10.4271/2007-01-0107
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Introduction | Tire Modelling
› Existing Methods− Rotating Wall (RW)
− Easy implementation
− Too inaccurate (no wall normal velocity)
− Moving Reference Frame (MRF)− Good for tire’s grooves
− Difficult to set up
− Sliding Mesh (SM)− Good for accurate rim/hub simulation
− Wheel deformation/road contact is challenging
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Introduction | Tire Modelling
› Existing Methods− Rotating Wall (RW)
− Easy implementation
− Too inaccurate (no wall normal velocity)
− Moving Reference Frame (MRF)− Good for tire’s grooves
− Difficult to set up
− Sliding Mesh (SM)− Good for accurate rim/hub simulation
− Wheel deformation/road contact is challenging
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› Combined SM for hubs + automated MRF for treads
− MRFg (Hobeika & Sebben)
› Generalized moving Reference Frame (GRF)
− Rotation approximation
− Good for tire's grooves
− Non circular patches
− Automated frame selection
T. Hobeika and S. Sebben, “CFD investigation on wheel rotation modelling,” Journal of Wind Engineering and Industrial Aerodynamics, vol. 174, pp. 241–251, Mar. 2018.
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GRF Methodology
GRF Verification
GRF (n)GRF (s)MRF
Method Ventilation Moment (Nm) Iterations
MRF 0.167 1866
GRF (s) 0.166 1761
GRF non-circular (n) 0.163 1243
› MRF vs GRF
› 𝜔 = 90 𝑟𝑎𝑑/𝑠
› circular vs non-circular zone boundary
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› Complex geometries make frame definitions difficult
› Automated detection− Convection equation is solved
− 𝛻 ⋅ (𝛷𝛺𝜏) = 0
− Tracer field indicates zone
› Enabled by GRF support for non-circular frame boundaries
› Remove need for mesh-zone
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GRF Methodology
Swept Cell Method
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› uRANS with k-OmegaSST
› ~7 million cells, 2mm surface face size
› 3 Configurations:− SM on the whole wheel
− RW on the whole wheel
− GRF on the grooves + SM for on the rim
› Similar ventilation moment prediction between SM and GRF
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Tire Modelling Results
Stand-alone wheel validation
SM RW GRF
Ventilation moments for three different configurations.
GRF zone automatically created with swept cell method
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› With kind permission of BMW AG
› PhD thesis− Schnepf, B., „Untersuchung von
Einflussfaktoren auf die Umströmung eines Pkw-Rades in Simulation und Experiment“, Dissertation, Technische Universität München, 2016
› Windtunnel campaign with moving ground at 140 km/h.
› Deformed tire
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Tire Modelling Results
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› Experimental data available
› Pressure and velocity measurements in various planes
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Tire Modelling Results
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› Automatic GRF cells selection with sweep method
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Tire Modelling Results
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Tire Modelling Results
Experiment
GRF
Rot Wall
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Tire Modelling Results
ExperimentGRF
Rot Wall
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› With kind permission of Volvo Cars
› Volvo S60
› Open and Closed Rim configurations− SM used for Open Rim
› Difference in drag coefficient between slick and detailed tires
› Compare with experimental values for
𝛥𝐶𝐷 = 𝐶𝐷 𝐷𝑒𝑡𝑎𝑖𝑙 − 𝐶𝐷 𝑆𝑙𝑖𝑐𝑘
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Tire Modelling Results
Full car simulation
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› Delayed Detached Eddy Simulation (DDES) Spalart-Allmaras turbulence model
› ~100 million cells
› Inlet velocity: 100 Km/h
› Average over 1 second
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Tire Modelling Results
Full car simulation
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Tire Modelling Results
Full car simulation
Rotating Wall GRF
› Slice across the wheel plane
› Difference in the velocity field in the vicinity of the grooves
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› Comparison of 𝛥𝐶𝐷› Good prediction for closed rims
› Ambiguous results for open rims
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Tire Modelling Results
Full car simulation
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Extended Reference Frames | Application
› Vehicle cornering through a chicane
› Vehicle max speed 100km/h
𝑇 = 0𝑠𝑈 = 0𝑘𝑚/ℎ
𝑇 = 3𝑠𝑈 = 100𝑘𝑚/ℎ
𝑇 = 4𝑠𝑈 = 100𝑘𝑚/ℎ
𝑅 = 15𝑚
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Extended Reference Frames | Application
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Conclusions
› For wheel modelling− Easy to set up and use− Accurate − GRF can support any shape and any motion
› For vehicle cornering− Globalized definition of reference frames− Nested frames support
› Future work: − sliding mesh interface automation− performance optimization− Extended reference frames for dynamic meshes− GUI support
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